Tap-off coupler with fixed attenuation for coaxial lines



Nov. 9, 1954 G. G. EDLEN ETAL 2,694,183

TAP-OFF COUPLER WITH FIXED ATTENUATION FOR COAXIAL LINES Filed Sept. 29, 1953 rillllllill lliiili iii] INVENTORS Geo/"g6 G. Ed/svv (I flan/"y M. D/Omb/"G Afforweg United States Patentfl TAP oFF coiJPLEn WITH FIXEU TIENUATION FOR CGAXIAL LINES George G. Edlen, Silver Spring,"Md;," and Henrv'Mj Diambr'a, Washington,"D.' C. ApplicationSeptember, 19s3,-sena1-No. 382,959-

9 Claims. (Cl.'33'3'-'-6') This invention relates to tap-off couplers for coaxial cables having a central inner conductor and a concentric braided outer conductor; the two being separated byisuitable insulation; andis an improvement of our earlier filed" U. S.patent application,Serial Number 338,104, filed February 20, 1953.

The objects and advantages of thepresent invention include the objects and advantages of the above identifiedearlier filed application, and include further the provision of arfimproved piercing :pin for'engagin'g the central conductor of acoaxial cable'whichis being tapped? An other-object is to improve the construction of the attenuating capacitor or resistor, or combination of both' which is provided'as'part of'the tap-off structure. A'further object is to improve theconstruction of the cableengagingblock' which engages the main coaxial cable and provides a support for the piercing pinand connector" to the tap-loif cable. Stillanother object is the provision of an improved mechanical and electrical connection be-' tween a tapoif cable and a connector.

The present-invention comprises a connecting block,'-- constructed to'closely engage and-firmly gripa main coaxial"cable,'and' provided with piercing 'points for insuring good electrical engagement with the outer "braided" conductor ofan engaged'coaxialcable." A threaded aperture isprovidedforreceiving-a tap-off coaxial cable connector having an insulated piercing point adapted to penetratethe outer braided conductor and to electrically contact the inner conductor ofthe' main coaxialcable when'thre'aded into said aperture' An attenuator; preferably' in the form of a'smallcapacitor, is provided in said-connector structure between the-piercing pin and the connection to a tap-off cable.

The main' 'connector block according to the' present invention'includes as part thereof unitary means for engaging a messenger wire such-as is commonly employed to support the -main coaxial cable. 1 Further unitary means are provided in the block for convenient attachment 'of a strain relief-line. By this construction, a simple'and unitary coupler is provided having all of'the necessary features for enabling a quick, efficient, and foolproof tap-oif -connection to 'be made to a main coaxial cable.

The/specific nature 'of the invention as well as other objects and advantages thereof will clearly appear from a description of a preferred embodiment as shown in the accompanying drawing, in which Fig. 1 is a side elevation of a tap-off connector-em bodying the invention;

Fig fi'2is a view taken on line 22 of Fig. 1; Fig. 3 is a view taken on line 33 of Fig32; Fig. 4 is a view taken on line 44 of Fig. 2; and

Fig-.'*5 is a diagrammatic view of a modified fo'rm'of capacitor-pin block."

Referring'to the figure'sfa metal block-'2 is provided to both the coaxial cables andthe messenger cable 10. Block 2 is provide'd'witha curvedcu't as'sh'own at'16 so as to leave a smoothly curved portion 18 for supporting a strain relief line 20 as best shown in Fig. 3. The strain relief 'line is attached in conventional fashion (not shown) -to tap-off coaxial-line 22'so that the mechanicah strain is-taken entirely'by messenger cable 10, block-2,

Patented Nov. 9, 1954 12, and strain line 20. Block 2 is provided withathread ed aperture 24 (Fig. 4) for threadedly receiving'tapmffconnector shell-26. Both block'Z and shell 26' are,'-of

course, made of good conductingmaterial; Sh'e'll'*26 is suitably ex'ternally'shapedat its central portion to form a nut- 28; The lower portion of the shell is externally. threaded to fit the correspondingly threadedaperture24 in block'2, andis internally bored to receive a'combined" piercing member and attenuating condenser, A, the con struction' of which differs materially from that disclosed" in our earlier filed application.

According to the present invention, the capacitor mem# her is formed of two plates '30 and 32 imbeddedin 'a' small block'36 of suitable insulating dielectric material;

Although any suitable 'insulatingymaterial: may. be employed, .a preferred material is that material-used in Y manufacturing the GA and QC capacitors available from? Stackpole Carbon Co. and'Quality Component lnc1, both of St. Marys, Pennsylvania.

The entire unit is molded-- under heat and pressure to form a unitary condenser hav ing a definite, fixed capacity of unchanging value. Block 36 is composed of a high-efiiciency,high-dielectric material whereby a reasonablylarge value of capacitance may Plate 32 may be formed be obtainedin a small volume.

by suitably heading wire 34 by means of a cold-forming operation, .and plate 34 may, of course, be similarly formed. The lateral edges of the plates may be grooved" as shown at 38 to ensure better engagement with the dielectric material 36.-

For some applications instead of a capacitor, it will be preferred to have a resistor.

This can be acco'tnplished in essentially the sameconstruction bymaking block '36 of suitable resistance material. For other app-lb cations, the combination'ofa resistor and capacitor may be desired. This, too, can be accomplished by making the block 36 of sufficiently high resistance materialso that some current leakage occurs, but not enough to overshadow the capacitive effect, whereby any desired proportion of capacitance to leakage resistance may be obtained.

It will be'seen thatthe element 32, 34 comprises a com-' As this pin in" bined piercing pin and capacitor plate.

use must pierce the outer braided conductor of the coaxial" cable, its outer surface must be insulated so that when" its point engages the central conductor 49 as shown "in Fig. 4, there will not be a short circuit between the outer braid 42 and the centralconductor 40. A highly satis factory insulating coating 46 is provided according to the invention by making pin 34 of aluminum and anodizing.

thesurface of the pin. Point 48 is formed by-grinding subsequent to the anodizing operation and is therefore."

of course, uninsulated. The anodizing is performed according to the standard commercial process of Metal Finishers, Inc., of Baltimore, Maryland, known as Martin Hard Coatj We have found thatthis process performed on aluminum of grade 568 provides an exceedingly hard coating having excellent insulating quality;'-

this coating is so hard that it is'diflicult to scratch even with a file. It is therefore excellently suited for the pres ent purpose.

Alternatively, other firmly bonded, thin,'--

abrasion-resistant insulating coatings utilizing a'chemical compound of the pin metal could be used, as many oxides have good mechanical and electrical properties for the present purpose, for example, Parkerizing in combination with a nylon, silicone, epoxy resin or varnish coating, could be'employed, although the anodized coating-de scribed above is preferred over any material we'have used.

Pin 50'of capacitor plate 30 is bored and split at its end as shown at 52 in orderto provide 'a well-known type of connection to solid central conductor'54 of tap-off cable 56.

The piercing connector may be assembled as follows: An insulating wafer 58, preferably of Teflon, is first insorted in the bore of shell 26 so that it rests against shouldet 60 of the shell. Wafer is centrally pierced to'acco'r'n modate pin 50 and is conically dished as shown at 62 so as to readily guide central conductor 54 into engagement with slotted end 52 of pin 50. Molded block 36 with its capacitor and pin elements is next inserted as shown. If the parts are accurately made, pin 46 will now be centered in the bore of shell 26, but in any case a suitable centering jig may be used to hold pin 46 accurately centered in the bore. A suitable casting resin 64 is now poured into the central bore, the unit being, of course, held inverted from the position shown in Fig. 4 so that the casting resin will be retained by gravity. A suitable casting resin for this purpose is Scotch Kast, made by Minnesota Mining & Manufacturing Co. of St. Paul, Minnesota. This material has excellent dielectric properties and very high mechanical strength and adherence, and serves to very rigidly cement together all of the elements and also to take the major portion of the mechanical strain which occurs when piercing pin 46 is forced through main cable 66 to engage its central conductor 40. Although the engagement of resin 64 with the walls of the shell bore is probably sufiicient for all practical purposes, we prefer to roll over the edge of the shell as shown at 68 (which may be done prior to adding the resin) in order to insure against the slightest possibility of the assembly loosening or coming out.

Alternatively, the piercing connector and capacitor assembly may be made up as a unit prior to insertion into the bore, any suitable resin being used as shown in Fig. 5. In this modification, a single outer casing 64a is provided which is firmly bonded at least to pin 46 so that any mechanical stress due to the piercing operation will be transmitted not to the block 36 (which is selected primarily for its electrical qualities rather than for its mechanical qualities) but to casing 64a, and thence to shoulder 60 of the shell 26.

Another alternative construction would be similar to that shown in Fig. 4 except that instead of casing 64 being poured in situ, it could be preformed externally of the shell 26 and assembled as shown, preferably with adhesive compound to form a rigid unit capable of relieving the capacitor dielectric of most of the mechanical stress. One reason for this precaution is, as previously noted, that block 36 is selected primarily for its electrical (rather than mechanical) properties.

An improved connection between cable 56 and shell 26 is provided by means of a wedge ring 70, which is forced down into annular recess 72 so as to firmly press outer insulation 74 and conducting braid 76 against the tubular shank 78 of shell 26. A length of braided outer conductor is left extending beyond the cut end of outer 1nsulation 74 and is turned back on itself in the recess, so that the outside surface of the wedge ring 70 engages it as shown at 76 and forces it into very tight engagement with the inner surface of the annular recess at 76. T1118 serves both to wedge the braid firmly into electrical contact with the shell, and also provides frictional engagement between the shell and braid so that it can withstand any strain which occurs in practical use. Moreover, the braid is caused to bite into the shell so firmly by the abovedescribed wedging action that even rotary sliding contact cannot occur, such as sometimes happens with other types of contacts.

Ring 70 is, of course, slipped over cable 56 prior to attachment of the cable. If desired, the ring may be provided with an axial or diagonal slit to accommodate itself to slight changes in diameter of the embraced portion, although a closed ring of suitable relative dimensions approximately as shown has been found to be quite satisfactory in performance. After the end of cable 56 has been prepared and is fitted to shank 78 as shown, the wedge ring is forced into place by any suitable means.

It will be apparent that the embodiments shown are only exemplary and that various modifications can be made in construction and arrangement within the scope of the invention as defined in the appended claims.

We claim:

1. A tap-01f for a coaxial cable of the type comprising conductive clamping means for firmly engaging a coaxial cable in electrical contact with the outer conductor thereof, a piercing terminal member supported by said clampmg means and insulated therefrom, having an insulated 8 piercing conductor terminating in a point for engagement with the central conductor of an engaged coaxial cable and having also a capacitor integrally connected to said piercing conductor, said capacitor comprising two parallel spaced conducting plate members, a block of highdielectric insulating material molded about said plate members and completely filling the space between them, one of said plate members being integrally connected to said piercing conductor, the other of said plate members having an integral linearly extending conductor portion axially aligned with said piercing member and extending oppositely therefrom, and means for connecting the central conductor of a tap-01f cable to the end of said linearly extending conductor.

2. The invention according to claim 1 including an element mechanically supported by said clamping means and having a bore opening toward and aligned with the central conductor of an engaged coaxial cable, said block and embedded conductors being retained within said bore with said piercing conductor extending out beyond the bore, and a casing of insulating material of high mechanical strength containing and supporting said block and piercing pin in said bore.

3. The invention according to claim 1, said piercing pin having a surface insulation comprising a chemically bonded layer of insulating material comprising a chemical compound of the pin material.

4. The invention according to claim 3, said chemical compound comprising an oxidation product of the pin material.

5. A tap-ofit' for a coaxial cable of the type comprising conductive clamping means for firmly engaging a coaxial cable in electrical contact with the outer conductor thereof, a threaded aperture in said clamping means, a threaded piercing terminal member supported by said clamping means in said aperture and having an insulated central piercing conductor terminating in a point for engagement with the central conductor of an engaged coaxial cable, and a capacitor integrally connected to said piercing conductor; said capacitor comprising two parallel spaced conducting plate members, a block of high-dielectric insulating material molded about said plate members and completely filling the space between them, one of said plate members being integrally conected to said piercing conductor, the other of said plate members having an integral linearly extending conductor portion axially aligned with said piercing conductor and extending oppositely therefrom, and means for connecting the central conductor of a tap-off cable to the end of said linearly extending conductor.

6. The invention according to claim 5, and a casing of insulating material of high mechanical strength containing and supporting said block and said piercing conductor.

7. The invention according to claim 6, said casing being firmly bonded to a portion of said insulated piercing conductor, whereby mechanical stress is transmitted mainly from the piercing conductor to the casing rather than to said block.

8. The invention according to claim 5, said threaded piercing terminal member comprising an outer shell having a central bore at one end thereof accommodating said block and embedded conductors with said piercing conductor extending out beyond said bore, said bore being of substantially larger diameter than said block, and a filling of solid plastic material of high strength and mechanical adherence mechanically supporting said block and conductors and firmly bonding them to the walls of said bore.

9. The invention according to claim 8, said bore being open at one end and leading to a reduced bore at the other end, thereby forming an annular shoulder at the junction of said two bores, a loose-fitting annular wafer of high- -dielectric insulating material in the first bore positioned against said shoulder and having a central aperture di mensroned to receive said linearly extending conductor.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,196,964 Lee Apr. 9, 1940 2,598,671 Boothby June 3, 1952 2,615,948 Kamen Oct. 28, 1952 2,677,108 Brady Apr. 27, 1954 

